The novel compounds of structure VIII (infra) are useful precursors to the previously disclosed compounds of structure IX (infra), shown in U.S. Pat. No. 3,952,033, which are in turn precursors to the compounds of structure X which are also disclosed in the aforementioned patent. A process related to the one disclosed in the instant application is found in Tetrahedron Letters No. 39, pp. 3555-3558, 1976 (G. Piancatelli et al.).